Autonomous transport vehicle

ABSTRACT

An autonomous transport vehicle including a frame having a longitudinal axis extending from a front of the frame to a back of the frame, at least one first guide member mounted on one side of the frame and having a first guide member frame of reference, and at least one second guide member mounted to an opposite side of the frame than the at least one first guide member and having a second guide member frame of reference, wherein the first and second guide members are asymmetrically compliant guide members so that a stiffness of the at least one first guide member in response to a force in a predetermined direction relative to the first guide member frame of reference is different than a stiffness of the at least second guide member in response to the force in the predetermined direction relative to the second guide member frame of reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/326,423, filed on Dec. 15, 2011 (now U.S. Pat. No. 5,561,905, andclaims the benefit of U.S. provisional patent application No.61/423,409, filed on Dec. 15, 2010, the disclosures of which areincorporated herein by reference in their entireties.

BACKGROUND

1. Field

The embodiments generally relate to storage and retrieval systems and,more particularly, to autonomous transports of the storage and retrievalsystems.

2. Brief Description of Related Developments

Warehouses for storing case units may generally comprise a series ofstorage racks that are accessible by transport devices such as, forexample, fork lifts, carts and elevators that are movable within aislesbetween or along the storage racks or by other lifting and transportingdevices. These transport devices may be automated or manually driven.Generally the items transported to/from and stored on the storage racksare contained in carriers, for example storage containers such as trays,totes or shipping cases, or on pallets.

It would be advantageous for the automated transport vehicle totransition between a physically unrestrained guide system and aphysically constrained guide system for transporting case units withinthe storage and retrieval system.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of the disclosed embodimentsare explained in the following description, taken in connection with theaccompanying drawings, wherein:

FIG. 1 schematically illustrates an exemplary storage and retrievalsystem in accordance with the embodiments;

FIG. 2 is a schematic illustration of a portion of the storage andretrieval system of FIG. 1 in accordance with the embodiments;

FIG. 3 illustrates a schematic illustration of an autonomous transportvehicle in accordance with the embodiments;

FIGS. 4A and 4B are exemplary illustrations of portions of theautonomous transport vehicle of FIG. 3 in accordance with theembodiments;

FIG. 5 is a schematic illustration of a portion of the storage andretrieval system of FIG. 1 in accordance with the embodiments;

FIGS. 6A and 6B are exemplary schematic force diagrams of forces appliedto the autonomous transport vehicle of FIG. 3 in accordance with theembodiments;

FIG. 7 is a schematic illustration of an autonomous transport vehiclewithin a picking aisle of the storage and retrieval system of FIG. 1 inaccordance with the embodiments; and

FIGS. 8A and 8B are exemplary schematic force diagrams of forces appliedto the autonomous transport vehicle of FIG. 3 in accordance with theembodiments.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT(s)

FIG. 1 schematically illustrates an exemplary storage and retrievalsystem 100 in accordance with the embodiments. Although the disclosedembodiments will be described with reference to the embodiments shown inthe drawings, it should be understood that the disclosed embodiments canbe embodied in many alternate forms. In addition, any suitable size,shape or type of elements or materials could be used.

In accordance with the embodiments the storage and retrieval system 100may operate in a retail distribution center or warehouse to, forexample, fulfill orders received from retail stores for case units(where case units as used herein means items not stored in trays, ontotes or on pallets, e.g. uncontained or items stored in trays, totes oron pallets). It is noted that the case units may include cases of items(e.g. case of soup cans, boxes of cereal, etc.) or individual items thatare adapted to be taken off of or placed on a pallet. In accordance withthe embodiments, shipping cases or case units (e.g. cartons, barrels,boxes, crates, jugs, totes, pallets or any other suitable device forholding case units) may have variable sizes and may be used to holditems in shipping and may be configured so they are capable of beingpalletised for shipping. It is noted that when, for example, bundles orpallets of case units arrive at the storage and retrieval system thecontent of each pallet may be uniform (e.g. each pallet holds apredetermined number of the same item—one pallet holds soup and anotherpallet holds cereal) and as pallets leave the storage and retrievalsystem the pallets may contain any suitable number and combination ofdifferent items (e.g. each pallet may hold different types of items—apallet holds a combination of soup and cereal). It should be understoodthat the storage and retrieval system described herein may be applied toany environment in which case units are stored and retrieved.

The storage and retrieval system 100 may be configured for installationin, for example, existing warehouse structures or adapted to newwarehouse structures. In the embodiments, the storage and retrievalsystem may include in-feed and out-feed transfer stations 170, 160,multilevel vertical conveyors 150A, 150B, autonomous transport vehicleor robot (referred to herein as “bots”) stations 140A, 140B, a storagestructure 130, and a number of bots 110. Suitable examples of storageand retrieval systems may be found in U.S. patent application Ser. No.12/757,220, filed on Apr. 9, 2010 (now U.S. Pat. No. 9,096,375), andU.S. patent application Ser. No. 12/757,381, filed on Apr. 9, 2010 (nowU.S. Pat. No. 8,740,538), and U.S. Provisional Patent Application No.61/423,340, filed on Dec. 15, 2010 (now U.S. Non-provisional patentapplication Ser. No. 13/326,674, filed on Dec. 15, 2011), thedisclosures of which are incorporated by reference herein in theirentireties. The in-feed transfer stations 170 and out-feed transferstations 160 may operate together with their respective multilevelvertical conveyors 150A, 150B for bi-directionally transferring caseunits to and from one or more vertically stacked levels of the storagestructure 130. It is noted that while the multilevel vertical conveyors150 are described herein as being dedicated inbound or in-feed conveyors150A and outbound or out-feed conveyors 150B, each of the conveyors150A, 150B may be used for both inbound and outbound transfer of caseunits/items from the storage and retrieval system. The multilevelvertical conveyors 150 may be any suitable lifting devices fortransporting case units between levels of the storage and retrievalsystem. It is noted that while multilevel vertical conveyors aredescribed herein in other aspects the conveyors may be any suitableconveyors or transfer/picking devices having any suitable transport pathorientation. Some non-limiting suitable examples of multilevel verticalconveyors can be found in, for example, U.S. Provisional PatentApplication No. 61/423,298, filed on Dec. 15, 2010, (now United StatesNon-provisional patent application Ser. No. 13/327,088 filed on Dec. 15,2011 (now U.S. Pat. No. 8,998,554), and U.S. Non-provisional patentapplication Ser. No. 12/757,354, filed on Apr. 9, 2010 (the disclosuresof which are incorporated by reference herein in their entireties) andU.S. Non-provisional patent application Ser. No. 12/757,220, filed onApr. 9, 2010 (now U.S. Pat. No. 5,096,375 and previously incorporated byreference). For example, the multilevel vertical conveyors 150A, 150Bmay have any suitable number of support shelves for transporting thecase units to a predetermined level of the storage and retrieval system100. The multilevel vertical conveyor support shelves may have slattedsupports configured to allow, for example, fingers 110F of a transferarm 110A (FIG. 3) of the bots 110 to pass between the slats fortransferring case units 101 (FIG. 2) to and from the conveyor 150. Caseunits may also be indirectly transferred between the bots 110 and themultilevel vertical conveyors 150A, 150B as described in, for example,U.S. patent application Ser. No. 12/757,220, filed on Apr. 9, 2010 (nowU.S. Pat. No. 9,096,375 and previously incorporated by reference). It isnoted that the transfer of case units between the bots 110 andmultilevel vertical conveyors may occur in any suitable manner.

As may be realized, the storage and retrieval system 100 may includemultiple in-feed and out-feed multilevel vertical conveyors 150A, 150Bthat are accessible by, for example, bots 110 on each of the stackedlevels of the storage and retrieval system 100 so that one or more caseunit(s) can be transferred from a multilevel vertical conveyor 150A,150B to each storage space on a respective level and from each storagespace to any one of the multilevel vertical conveyors 150A, 150B on arespective level. The bots 110 may be configured to transfer the caseunits between the storage spaces on storage racks 600 (FIG. 2) and themultilevel vertical conveyors with one pick (e.g. substantially directlybetween the storage spaces and the multilevel vertical conveyors). Byway of further example, the designated bot 110 picks the case unit (s)from a shelf of a multilevel vertical conveyor, transports the caseunit(s) to a predetermined storage area of the storage structure 130 andplaces the case unit (s) in the predetermined storage area (and viceversa).

The bots 110 may be configured to place case units, such as the abovedescribed retail merchandise, into picking stock in the one or morelevels of the storage structure 130 and then selectively retrieveordered items for shipping the ordered items to, for example, a store orother suitable location. As described above, in the embodiments, thebots 110 may interface in any suitable manner with the multilevelvertical conveyors 150A, 150B such as through, for example, extension ofa transfer arm 110A (FIG. 3) of the bot (which may have fingers 110F forinterfacing with slatted support shelves of the multi-level verticalconveyors) relative to a frame of the bot. The bot may also interfacewith the multilevel vertical conveyors indirectly in any other suitablemanner. Suitable examples of bots are described in U.S. Non-provisionalpatent application Ser. No. 12/757,312, filed on Apr. 9, 2010 (now U.S.Pat. No. 8,425,173), U.S. Provisional Patent Application No. 61/423,220,filed on Dec. 15, 2010 (now U.S. Non-provisional application Ser. No.13/327,040, filed on Dec. 15, 2011, (now U.S. Pat. No. 9,187,244)), U.S.Provisional Patent application Ser. No. 61/423,365, filed on Dec. 15,2010 (now U.S. Non-provisional patent application Ser. No. 13/326,952,filed on Dec. 15, 2011), U.S. Provisional Patent Application No.61/423,388, filed on Dec. 15, 2010 (now U.S. Non-provisional patentapplication Ser. No. 13/326,993, filed on Dec. 15, 2011 (now U.S. Pat.No. 9,499,338)), U.S. Provisional Patent Application No. 61/423,359,filed on Dec. 15, 2010 (now U.S. Non-provisional patent application Ser.No. 13/326,447, filed on Dec. 15, 2011 (now U.S. Pat. No. 8,965,619)),and U.S. Provisional Patent Application No. 61/423,206, filed on Dec.15, 2010 (now U.S. Non-provisional patent application Ser. No.13/327,035, filed on Dec. 15, 2011 (now U.S. Pat. No. 9,008,884)), thedisclosures of which are incorporated by reference herein in theirentireties.

The storage structure 130 may include multiple levels of storage rackmodules 600 (FIG. 2) where each level includes an array of storagespaces (arrayed on the multiple levels and in multiple rows on eachlevel), picking aisles 130A formed between the rows of storage spaces,and transfer decks 130B. In the embodiments, the picking aisles 130A andtransfer decks 130B may be arranged for allowing the bots 110 totraverse respective levels of the storage structure 130 for placing caseunits into picking stock and to retrieve the ordered case units. As maybe realized, the storage and retrieval system may be configured to allowrandom accessibility to the storage spaces. For example, all storagespaces in the storage structure 130 may be treated substantially equallywhen determining which storage spaces are to be used when picking andplacing case units from/to the storage structure 130 such that anystorage space of sufficient size can be used to store items. The storagestructure 130 of the exemplary embodiments may also be arranged suchthat there is no vertical or horizontal array partitioning of thestorage structure. For example, each multilevel vertical conveyor 150A,150B may be common to all storage spaces (e.g. the array of storagespaces) in the storage structure 130 such that any bot 110 can accesseach storage space and any multilevel vertical conveyor 150A, 150B canreceive case units from any storage space on any level so that themultiple levels in the array of storage spaces substantially act as asingle level (e.g. no vertical partitioning). The multilevel verticalconveyors 150A, 150B can also receive case units from any storage spaceon any level of the storage structure 130 (e.g. no horizontalpartitioning). It is noted that the storage and retrieval system mayalso be configured so that each multilevel vertical conveyor serves apredetermined area of the array of storage spaces. Suitable exemplaryconfigurations of storage and retrieval systems can be found in, forexample, U.S. Non-provisional patent application Ser. No. 12/757,381,filed on Apr. 9, 2010, (now U.S. Pat. No. 8,740,538), the disclosure ofwhich is incorporated by reference herein in its entirety.

The storage structure 130 may also include charging stations 290 forreplenishing, for example, an electricity storage device of the bots 110as described in, U.S. Provisional Patent Application No. 61/423,402,filed on Dec. 15, 2010 (now U.S. Non-provisional patent application Ser.No. 13/326,823, filed on Dec. 15, 2011 (now U.S. Pat. No. 9,082,112)),the disclosures of which are incorporated by reference herein in theirentireties.

The bots 110 and other suitable features of the storage and retrievalsystem 100 may be controlled by, for example, one or more central systemcontrol computers (e.g. control server) 120 through, for example, anysuitable network 180. The network ISO may be a wired network, a wirelessnetwork or a combination of a wireless and wired network using anysuitable type and/or number of communication protocols. It is notedthat, in the embodiments, the system control server 120 may beconfigured to manage and coordinate the overall operation of the storageand retrieval system 100 and interface with, for example, a warehousemanagement system 125, which in turn manages the warehouse facility as awhole. The control server 120 may be substantially similar to thatdescribed in, for example, U.S. Non-provisional patent application Ser.No. 12/757,337, filed on Apr. 9, 2010 (now U.S. Pat. No. 8,594,835), thedisclosure of which is incorporated by reference herein in its entirety.

Referring now to FIG. 2, a portion of one level 100L of the storage andretrieval system 100 is shown. As may be realized substantially similarlevels may be located above and/or below level 100L to form an array ofvertically stacked storage levels as described above. In the embodimentseach level 100L may have a transfer deck 130B and one or more pickingaisles 130A1-130A7. Storage racks 600 may be disposed on either side ofeach picking aisle 130A1-130A7 so that case units 101 may be stored onboth sides of each picking aisle.

The transfer deck 130B may be configured to allow generally physicallyunrestrained travel of the bots 110 while on the transfer deck 130B. Forexample, the transfer deck 130B may have any suitable number of travelguide lines 130L1-130L4 and any suitable number of shunt, or bypassguide lines 130S1-130S7 that form one or more travel paths or lanes forthe bots 110 to traverse. For example, guide lines 130L1, 130L2 allowtravel in a first direction and guide lines 130L3, 130L4 allow travel ina second direction substantially opposite the first direction. It isnoted that while the direction of travel along a respective guide line130L1-130L4 is generally in a single direction, the guide lines, incombination with for example suitable bot traffic management, may allowfor limited bidirectional travel of the bots 110 along the guide lines130L1-130L4 as described below. In the embodiments bot traffic may bemanaged through, for example, bot-to-bot communications and/or trafficmay be managed by bot location tracking and management through, forexample, control server 120 or other suitable controller of the storageand retrieval system. A suitable example, of bot traffic management maybe found in, for example, U.S. Non-provisional patent application Ser.No. 12/257,337, filed on Apr. 9, 2010 (now U.S. Pat. No. 8,594,835), thedisclosure of which is incorporated by reference herein in its entirety.

Shunt guide lines 130A1-130S7 may also be arranged on the transfer decktransverse to the guide lines 130L1-130L4 for allowing the bots 110 tobi-directionally switch between guide lines 130L1-130L4 and enter thepicking aisles 130A1-130A7. The shunt guide lines 130S1-130S7 areoriented substantially transverse to the travel guide lines 130L1-130L4.The shunt guide lines 130S1-130S7 may allow bots access to, for example,the picking aisles 130A or the bot stations 140 without traversing anentire length of the travel guide lines 130L1-130L4. In the embodiments,the shunt guide lines may be aligned with the picking aisles 130A1-130A7or any other suitable ingress or egress location of the storage andretrieval system allowing the bot to turn down a corresponding pickingaisle while travelling along any one of the travel guide lines13GL1-130L4. It is noted that the shunt guide lines 130S1-130S7 may alsobe located at ends of the transfer deck 130B or at any other suitablelocations of the transfer deck 130B. The shunt guide lines 130A1-130S7may also be used to track a position of the bot 110 through the storageand retrieval system structure and monitor travel along the travel guidelines 130L1-130L4. For example, the position of the shunt guide lines130A1-130S7 may be recorded in a memory accessible by or within controlserver 120 and the bots 110 may be configured to detect and send signalscorresponding to the shunt guidelines 130A1-130S7 to the control server120 so that a position of the bot and whether one or more bots aremoving along e.g. the travel guide lines 130L1-130L4 can be determinedby the control server.

Bot station guide lines 130C1-130C3 may also be provided on the transferdeck 130B for allowing the bots 110 to enter the bot stations 140 forinterfacing with a respective multilevel vertical conveyor 150 from anyone of the guide lines 130L1-130L4. The conveyor access guide lines130C1-13GC3 may be substantially similar to the shunt guide lines130S1-130S2. In this example the entrance/exit guide lines 130C1, 130C2of the bot station 140 are shown as not being aligned with any of theshunts 130S1-130S7 but in other embodiments the entrance/exit guidelines for the bot stations 150 may be substantially aligned with theshunts (see e.g. guide line 130S7) so that, where a course of travelpermits, bots 110 can travel directly from a picking aisle to a botstation and vice versa. It is noted that while the embodiments of thetransfer deck 130B and bot stations 140 are described herein withrespect to line following, the transfer deck 130B and bot stations 140may be configured so that the bots are guided by any suitable railsystem.

Referring also to FIG. 3 Each bot 110 may employ a combination of guideand positioning systems, for example, line following (e.g. on thetransfer deck 130B) and rail guidance (e.g. within the picking aisles).The storage and retrieval system may be configured to allow the bot totransition between the structurally deterministic or restrained guidesystem within, for example, the picking aisles and the unrestrainedguidance system of, for example, the transfer decks. The transitionsbetween the guidance systems may also include a change in botorientation (e.g. front end leading the direction of travel or the frontend trailing the direction of travel). Each bot 110 may include anysuitable guides mounted to a frame 300 of the bot 110 where the guidesare configured to engage the restrained guidance system in apredetermined and repeatable manner to allow for an accurate andpredetermined reach of a transfer arm 110A of the bot 110 fortransferring case units 101 between the bot 110 and, for example, astorage shelf 600. The guides may also, at least in part, facilitate thetransition between the unrestrained and restrained guidance systems.

Each bot 110 may include a frame 300, independently driven drive wheels1211, 1212 and, for example lockable caster wheels 1261, 1262. It isnoted that the bot may have any suitable drive for driving the drivenwheels and/or any suitable steering mechanism for turning steeringwheels of the bot 110. It is noted that the general direction of travelof the bots 110 may be with the front end 320 leading the direction oftravel with the caster wheels 1261, 1262 locked as described in U.S.Non-provisional patent application Ser. No. 13/326,447, filed on Dec.15, 2011 (now U.S. Pat. No. 8,965,619), previously incorporated byreference herein, so that the bot may stably travel at substantiallyhigh speeds. At lower speeds the bot may travel with the front endleading or the front end trailing. The bot can also be configured to bedriven with unlocked casters by any suitable control system on-board thebot or located remotely from the bot.

The frame 300 may have a front end 320 and a back end 321 longitudinallyseparated from the front, end 320. The frame 300 may form a payloadholding area 310 having an extendable arm 100A configured to extend andretract in the direction of arrow 301. The arm 110A may havecantilevered fingers 110F for supporting case units when transferringthe case units to and from the bot 110. The fingers 110F may be arrangedto fit between slatted supports on the storage shelves 600 andmultilevel vertical conveyor 150 shelves for transferring case units toand from the storage shelves 600 and multilevel vertical conveyors 150.It is noted that the bot arm 110A may have any suitable configurationfor transferring case units to and from the bot 110. In the embodimentsthe arm 110A of the bot 110 is configured for extension on one lateralside of the bot 110 (e.g. the picking side of the bot on which a pickfence 305 is located where the case units may be lifted over the pickfence during transfer to and from the bot and the pick fence may be usedto hold case units on the bot 110 during transport). It is noted that,the arm 110A may be configured for extension on both lateral sides ofthe bot. Where the arm 110A extends to one side of the bot 110, the botorientation (e.g. front end leading or front end trailing) with respectto the direction of travel of the bot 110 is accounted for so that theextension direction of the arm 110A is located on the side of thepicking aisle 130A1-130A7 or bot station at which the case units are tobe picked from or transferred to.

The bot 110 may also have any suitable number of sensors 110S forsensing the guide lines 130L1-130L4, 130S1-130S7, 130C1-130C3 asdescribed in, for example. U.S. Non-provisional patent application Ser.No. 13/326,823, filed on Dec. 15, 2011 (now U.S. Pat. No. 9,082,112) andU.S. Non-provisional patent application Ser. No. 12/757,312, filed onApr. 9, 2010 (now U.S. Pat. No. 8,425,173), previously incorporated byreference herein. It is noted that the bot can at times drive withoutthe use of guide lines through any means of control such as, forexemplary purposes only, dead reckoning, state estimation, and use ofgyroscopes and accelerometers.

The bots 110 may have any number of suitable guide wheels 351-354 forguiding the bot 110 into and along the picking aisles 130A1-130A7.Suitable guide wheel/rail interaction is described in, for example, U.S.Pat. Nos. 8,425,173, 8,740,538, and 9,096,375, previously incorporatedby reference. It is noted that the guide wheels 351-354 may interfacewith any suitable guides in any suitable manner. While guide wheels areshown in the Figs. in other aspects it should be understood that the botmay include any suitable guide members having, for example, atwo-dimensional pivot offset and a one-dimensional pivot offset. It isfurther noted that one or more of the guide members may have a differentspring rate than other ones of the guide members. Referring also toFIGS. 4A and 4B the bot may include pairs of guides, such as forexample, guide wheels 351-354 located at the outer-corners of the botframe 300. While the guides are described herein as being guide wheelsin alternate embodiments any suitable type of guides may be used. Onepair of guides may be located at each end of the bot 110. For example,guide wheels 351, 352 may be located at a front 320 of the bot whileguide wheels 353, 354 are located at a back of the bot 110. Each guidewheel pair may include a substantially compliant guide wheel 352, 353and a substantially fixed guide wheel 351, 354 located on opposite sidesof the bot 110. For exemplary purposes only in the embodiments thesubstantially fixed guide wheels may be located on a side of the botfrom which the transfer arm extends 110A. In the embodiments thesubstantially fixed guide wheels may alternatively be located on theside of the bot opposite the side from which the bot arm extends. It isnoted that in the embodiments, the substantially fixed and substantiallycompliant guide wheels may have any suitable locational arrangement onthe bot.

As shown in FIG. 4A the substantially compliant guide wheels 352, 353may be pivotally mounted to the bot 110 on a mounting member 400 and mayinclude a pivot member 401, a bumper 402, a guide wheel fork 403, wheel404 and wheel retainer 405. In the embodiments, the guide wheel fork 403is pivotally mounted at a first end to the mounting member 400 by pivotmember 401. The pivot member may be any suitable axle or pivot. Thewheel 404 is rotatably mounted to a second end of the guide wheel fork403 by wheel retainer 405. The wheel retainer 405 may be any suitableaxle or other retaining mechanism. The bumper 402 may be any suitableshock absorber that, is mounted between the bot frame 300 and the wheel404 for substantially limiting the travel of the wheel 404 whileallowing the wheel to rotate about wheel retainer 405. It is noted thatin the embodiments the substantially compliant guide wheels may have anysuitable configuration.

As shown in FIG. 4B the substantially fixed guide wheels 351, 354 mayalso be pivotally mounted to the bot 110 on a mounting member 450 andmay include a pivot member 451, a bumper 452, a guide wheel fork 453,wheel 454 and wheel retainer 455. In the embodiments, the guide wheelfork 453 is pivotally mounted at a first end to the mounting member 450by pivot member 451. The pivot member may be any suitable axle or pivot.The wheel 454 is rotatably mounted to a second end of the guide wheelfork 453 by wheel retainer 455. The wheel retainer 455 may be anysuitable axle or other retaining mechanism. The bumper 452 may be anysuitable shock absorber or other suitable resilient member that ismounted between the bot frame 300 and the wheel 454 for substantiallylimiting the travel of the wheel 454 and absorbing forces applied to thebot 110 while allowing the wheel to rotate about wheel retainer 455. Itis noted that in the embodiments the substantially fixed guide wheelsmay have any suitable configuration.

Referring to both FIGS. 4A and 4B it is noted that the axis of rotationR1, R3 of the wheels 404, 454 relative to the axis of rotation R2, R4 ofthe guide wheel forks 403, 453 for the substantially compliant guidewheels 352, 353 and the substantially fixed guide wheels 351, 354 may bedifferent. For example, the axis of rotation R1 of the substantiallycompliant guide wheels 352, 353 may be longitudinally offset by adistance Y1 from the axis of rotation R2 of the guide wheel fork 403while the axes of rotation R3, R4 for the substantially compliant guidewheels 351, 354 are located substantially longitudinally aligned witheach other. These guide wheel configurations may allow both guide wheelsto rotate about respective axes R2, R4 while entering, for example, apicking aisle 130A1-130A7. However, when travelling within the pickingaisle 130A1-130A7 these configurations may maintain substantially fixedguide wheels 351, 354 substantially fixed about axis R4 and allow thesubstantially compliant guide wheels 352, 353 to rotate about axis R2.As may be realized, the guide wheels are asymmetrically compliant guidemembers so that a stiffness of the at least one first guide member inresponse to a force in a predetermined direction relative to the firstguide member frame of reference (e.g. in an X-Y plane) is different thana stiffness of the at least second guide member in response to the forcein the predetermined direction relative to the second guide member frameof reference (e.g. in an X-Y plane) as will be described in greaterdetail below.

Referring also to FIGS. 2, 5, 6A and 6B each of the guide wheels 351-354may be configured to interface with lead-in structures or guides of thestorage and retrieval system 100. For example, in one exemplaryembodiment a pair of angled guide members 500, 501 may be positioned atleast partially on the transfer deck 130B in a transition area fortransitioning between the transfer deck and, for example, a pickingaisle. The angled guide members 500, 501 may be any suitable guidemembers having any suitable configuration for cooperating with one ormore guide wheels 351-354 and at least in part directing a bot 110 intothe picking aisle 130A. For example, bot 110N may be travelling alongguide line 130L4 (which provides a general direction of travel in thedirection of arrow 298) to pick/place a case unit 101 in picking aisle130A7. In the embodiments the case unit may be located on the left side260 of the aisle 130A7. As can be seen in FIG. 5 the bot transfer arm110, in this example, is configured to extend to the left side of thebot 110 (with respect to a longitudinal or Y axis of the bot definedbetween the front and back ends 320, 321). As such, for the bot topick/place a case unit 101 from the left side 260 of the picking aisle130A7 the bot travels down the picking aisle with the front end 320leading the direction of travel. As the bot turns down the picking aisle130A7 a differential torque is applied to the independently driven drivewheels 1211, 1212 causing the front end 320 of the bot to swing in thedirection of arrow 270. As the front end 320 of the bot 110 turns in thedirection of arrow 270 substantially compliant guide wheel 352 maycontact the angled guide member 501. The contact between thesubstantially compliant, guide wheel 352 and guide member 501 may assistthe bot 110 in aligning with the guide rails 550, 551 of the pickingaisle. For example, as the bot 110 continues to turn, the guide members500, 501 form a funnel-like arrangement such that contact between thesubstantially compliant guide member 352 effects contact betweensubstantially fixed contact member 351 and guide member 500. As the botmoves further into the picking aisle guide wheels 353, 354 may also comeinto contact with their respective guide members 500, 501 for alignmentwith the guide rails 550, 551. As may be realized, during guided travelof the bot, guide wheels of the bot do not always have to be in contactwith the guide rails. For example, tolerance variations, bends in therails, variations in assembly of the storage structure may cause theguide wheels to temporarily break contact with a surface of the guiderails. It is noted that the guide rail system could include a system ofopposing magnetic fields (e.g. the bot includes a magnetic fieldgenerator and the storage structure includes a magnetic field generatoreach having opposing polarities) that are configured to maintain atravel path of the bot without providing any substantial resistance tobot motion along the travel path.

When the substantially compliant guide wheel, such as guide wheel 352contacts the guide member 501 forces 601, 602 are applied by the guidemember 501 to the wheel 404 in both the X and Y directions, where the Ydirection is parallel with the longitudinal axis (e.g. front to back) ofthe bot 110 and the X direction is transverse (e.g. substantiallyparallel with the lateral axis of the bot 110) to the Y direction. Theseforces 601, 602 are transferred to the wheel retainer 405 as translatedforces 601A, 602A. These translated forces 601A, 602A cause resultantforces 601R, 602R to be exerted in both the X and Y directions by thesubstantially compliant guide wheel back towards the guide member 501.Because the axis of rotation of the guide wheel retainer 405 islongitudinally offset (e.g. in the Y-direction) from the axis ofrotation R2 of the pivot member 401 by the distance Y1 (FIG. 4A) theforces exerted on the guide wheel cause a rotating moment 610 such thatthe wheel fork 403 (and wheel 404) rotates about the pivot member 401 inthe direction of arrow 611. The bumper 402 may in part, resist or absorbthe translated forces applied to the guide wheel and provide at least inpart some resistance to the rotating moment 610. It is noted that asimilar moment may be generated on substantially compliant guide wheel352 as the guide wheel 352 contacts the guide member 501 and the back321 of the bot comes into alignment with the guide rails 550, 551.

As the substantially fixed guide wheel, such as guide wheel 351 contactsthe guide member 500 forces 621, 622 are applied by the guide member 501to the wheel 404. These forces 621, 622 are transferred to the wheelretainer 455 as translated forces 621A, 622A. These translated forces621A, 622A cause resultant forces 621R, 622R to be exerted in the Xdirection by the substantially compliant guide wheel back towards theguide member 500. Because of the arrangement of the wheel retainer 455and pivot member 451 being laterally aligned only the forces in the Ydirection may contribute to creating a rotating moment 612 such that thewheel fork 453 (and wheel 454) rotates about the pivot member 451 in thedirection of arrow 613. The bumper 452 may in part resist or absorb thetranslated forces applied to the guide wheel and at least in part resistthe rotating moment 612. It is noted that a similar moment may begenerated on substantially fixed guide wheel 354 as the guide wheel 354contacts the guide member 500 and the back 321 of the bot comes intoalignment with the guide rails 550, 551.

Referring to FIGS. 7, 8A and 8B, once in the picking aisle 130A theguide wheels 351-354 may ride along vertical portions 550W of the guiderails 550, 551 for positioning the bot 110 a predetermined distance X1from the case units 101 stored on the storage shelves 600. In thisexample, the distance X1 is determined between the pick fence 305 of thebot 110 and a predetermined datum plane D along which the case units 101may be aligned. When in the picking aisle 130A the vertical portion 550Wof rail 550 may exert a force 801 in the X direction against the wheel454 of substantially fixed guide wheel, such as guide wheel 351. Aresultant force 802 may be applied by the substantially fixed guidewheel 351. Because of the axis of rotation R3 of the wheel retainer 455,the axis of rotation R4 of the pivot member 451 and the force 801, 802being along the same lateral (e.g. X direction) line the substantiallyfixed guide wheel remains substantially rigid without any rotatingmoments being applied to the guide wheel 351. Similar forces may begenerated on and by substantially fixed guide wheel 354. Because thereare no rotating moments applied to the substantially fixed guide wheels351, 354 while in the picking aisles the rigid arrangement of the guidewheels 351, 354 maintains, for example, the pick fence 305 of the bot110 at the predetermined lateral distance X1 away from the datum planeD.

The forces exerted on the substantially compliant guide wheels, such asguide wheel 352, in the picking aisles 130A may be substantially similarto those described above with respect to the substantially fixed guidewheels 351, 354. For example, the vertical portion 551W of guide rail551 may exert force 803 in the X direction against the wheel 405 whichresults in a resultant force 804 being generated by the guide wheel 352.Because the axis of rotation R1 of the wheel retainer 405 (e.g.substantially the point at which the force 803 is applied) islongitudinally offset from the axis of rotation R2 of the pivot member401 a rotating moment 810 is generated causing the wheel 404 (and wheelfork 403) to pivot in the direction of arrow 811 about pivot member 401.The wheel 404 may continue to pivot about pivot member 401 untilsubstantially stopped by the bumper 402. It is noted that similar forcesmay be generated against and to the substantially compliant guide wheel353. The forces (e.g. the resultant force 804) applied in this example,by the bumpers 804 of their respective substantially complaint guidewheels 352, 353 in combination with the compliant rotation of therespective wheel forks 403 about respective pivot members 401 causes thebot 110 to be pushed laterally so that the substantially fixed guidewheels 351, 354 are held against the vertical portion 550W of the guiderail 550 for maintaining the distance X1.

Referring to FIG. 2, as an example of bot travel, a bot 110Y travellingalong a path corresponding to guide line 130L1 may be instructed totransfer an item to a storage location in picking aisle 130A5. However,the bot 110Y may have already passed the shunt guide line 130S5corresponding to picking aisle 130A5. The bot may continue to travelalong guide line 130L1 until it encounters the next available shunt(e.g. a shunt not being used by another bot) such as shunt guide line130S4. The bot may turn onto shunt guide line 130S4 and then turn ontoone of the guide lines 130L3, 130L4 so that the bot 110 is travelling insubstantially the opposite direction towards the picking aisle 130A5.The bot may continue to travel along one of the guide lines 130L3, 130L4until it encounters shunt guide line 130S5, corresponding to pickingaisle 130A5, where the bot turns onto shunt guide line 130S5 fortransitioning into or otherwise entering the picking aisle 130A5 guideway (such as, for example, a rail guidance system).

As described above, the direction (e.g. front end leading or front endtrailing) the bot enters the picking aisle may depend on which side ofthe picking aisle a case unit is to be picked from or placed to. In theexamples above with respect to bots 110N, 110Y the bot entered thepicking aisles with the front end 320 leading. The travel paths definedby guide lines 130L1-13L4 may provide at least limited bidirectional bottravel for allowing the bot to enter the picking aisle with the frontend 320 trailing the direction of travel. For example, still referringto FIG. 2 the bot 110M may be designated to transfer a case unit to theright side 261 of picking aisle 130A4. However, when travelling alongany one of the guide lines 130L1-130L4 if the bot were to turn ontoguide line 130S4 for transitioning into the picking aisle 130A4 with thefront end 320 leading the direction of travel the transfer arm extensionwould be located on the wrong side of the aisle. It is noted that thebot could be fitted with any suitable device such as a turntable thatcould pivot or rotate the bot's payload bed within the bot allowing forthe extension arms of the bot to be positioned for extension/retractionon the correct side of the aisle. The bot 110M may be configured so thatthe bot 110M travels past the picking aisle 130A4 along, for example,guide line 130L4. Any suitable bot collision avoidance or other trafficmanagement may allow the bot 110M to travel in the direction of arrow271 (e.g. substantially opposite the direction of the general trafficflow along guide path 130L4 as indicated by arrow 298) so that the botcan enter the picking aisle, in a manner substantially similar to thatdescribed above, with the back end 321 leading the direction of travel(e.g. the front end 320 trailing the direction of travel). As may berealized the guide members 500, 501 (FIG. 5) may be configured to guidethe bot 110M into the picking aisle 130A4 with the bot travellingforwards (with the front end leading the direction of travel) orbackwards (with the back end leading the direction of travel) where theinteraction between the substantially fixed guide wheels 351, 354 andsubstantially compliant guide wheels 352, 353 and the guide members 500,501 occurs in a manner substantially similar to that described above. Itis noted that the arrangement of the fixed guide wheels 351, 354 and thesubstantially compliant guide wheels 352, 353 may be such that thesubstantially fixed guide wheels are located on the inside of the botturns when entering, for example, the picking aisles (and/or the botstations as described below).

As may be realized, the bots exiting the picking aisles may do so witheither the front end 320 leading or trailing the direction of travel.For example, where each picking aisle 130A has a single lane of travelthe bot may exit the picking aisle in the opposite orientation in whichthe bot entered the picking aisle. For example, bot 110M may enterpicking aisle 130A4 with the back end 321 leading the direction oftravel as described above and may exit the picking aisle 130A4 with thefront end leading the direction of travel.

In the embodiments the bot station 140 may be in the form of a vestibule130V that extends between the transfer deck 130B and the multilevelvertical conveyor 150. Each vestibule 130V may be configured with morethan one charging/transfer station 290A, 290B (generally referred toherein as stations). Each of the stations 290A, 290B may be configuredto charge an electricity storage device of the bot as well as serve as atransfer location for accessing a respective portion of the multilevelvertical conveyor shelf 250. The stations 290A, 290B may be arranged in,for example, a linear array, along guide line 130C2. It is noted thatthere may be any suitable number of stations having any suitablearrangement within the vestibule 130V. To allow the bots 110 access toeach of the stations 290A, 290B the guide lines 130C1-130C3 of thevestibule 130V may be configured to allow bidirectional travel of thebots 110 (in combination with, for example, suitable bot trafficmanagement).

In one example, general travel through the vestibule 130V may be suchthat the bots 110 enter the vestibule on guide line 130C3, travelthrough the vestibule along guide line 130C2 and exit the vestibulealong guide line 130C1. The bot 110Y may be designated for transferringa case unit to the multilevel vertical conveyor 150 at station 290A.However, a bot 110X may be located at station 290B blocking access tothe station 290A along the general direction of travel through thevestibule 130V. The bot 110Y may travel along guide line 130L1 in thedirection of arrow 299 past vestibule guide line 130C1. The bot may turnonto the guide line 130C1 and enter the vestibule with the back endleading the direction of travel in a manner substantially similar tothat described above with respect to bot 110M entering picking aisle130A4. It is noted that in the embodiments the entrances/exits of thevestibule 130V may include guide members substantially similar to guidemembers 500, 501 described above with respect to FIG. 5 such that theguide members 500, 501 assist, for example, the line following of thebot. In alternate embodiments the entrances/exits of the vestibule 130Vmay lack guide members such that transition into the vestibule occursthrough line following. Once on the guide line 130C1 the bot may traveland turn on to guide line 130C2 for arriving at station 290A so that atransfer of case unit 101 may be made between the bot 110Y and themultilevel vertical conveyor 150.

Similarly, if bot 110X completes the transfer of case unit 101 atstation 290B while bot 110Y is located at station 290A the exit of thevestibule (as determined from the general flow of traffic through thevestibule described above) may be blocked. The bot 110X may travel withthe back end 321 leading the direction of travel so that the bot 110Xexits the vestibule along guide line 130C3. It is noted that thevestibule, such as vestibule 130V may include multiple substantiallyparallel paths or guide lines 130C3, 130C4 through the vestibule whereshunts 130S traverse the paths 130C3, 130C4. The bots 110 may use theseparallel paths 130C3, 130C4 and shunts 130S to travel around botslocated at one or more of the stations 290A, 290B for accessing adesired one of the (unoccupied) stations 290A, 290B.

In a first aspect of the disclosed embodiment an autonomous transportvehicle is provided. The autonomous transport vehicle includes a framehaving a longitudinal axis extending from a front of the frame to a backof the frame, at least one first guide member mounted on one side of theframe and having a first guide member frame of reference, and at leastone second guide member mounted to an opposite side of the frame thanthe at least one first guide member and having a second guide memberframe of reference, wherein the first and second guide members areasymmetrically compliant guide members so that a stiffness of the atleast one first guide member in response to a force in a predetermineddirection relative to the first guide member frame of reference isdifferent than a stiffness of the at least second guide member inresponse to the force in the predetermined direction relative to thesecond guide member frame of reference.

In accordance with a first sub-aspect of the disclosed embodiment, theat least one first guide member includes a first yoke pivotally mountedto the frame about a first pivot member and a first engagement membermounted to the first yoke, and the at least one second guide memberincludes a second yoke pivotally mounted to the frame about a secondpivot member and a second engagement member mounted to the second yoke.

In accordance with the first sub-aspect of the first aspect of thedisclosed embodiment, the first engagement member is longitudinallyoffset, from the first pivot member.

In accordance with the first sub-aspect of the first disclosedembodiment, the second engagement member is transversely aligned withthe second pivot member.

In accordance with the first aspect of the disclosed embodiment one ormore of the at least one first and at least one second guide memberscomprise rotatable wheels.

In accordance with the first aspect of the disclosed embodiment, the atleast one first guide member comprises two first guide members and theat least one second guide member comprises two second guide members, thetwo first guide members being located on a first side of the autonomoustransport vehicle and the two second guide members being located on asecond opposite side of the autonomous transport vehicle.

In accordance with the first aspect of the disclosed embodiment, theautonomous transport vehicle is configured for transporting item betweenthe autonomous transport vehicle and storage shelves of a storage andretrieval system and the at least one second guide member is configuredto maintain a predetermined transverse distance between the autonomoustransport vehicle and the items stored on the storage shelves.

In accordance with a second sub-aspect of the first aspect of thedisclosed embodiment, the at least one first and at least one secondguide members are configured to interface with a first guide rail and asecond guide rail of a storage and retrieval system where the first andsecond guide rails are located on opposite sides of the autonomoustransport vehicle for guiding the autonomous transport vehicle along asubstantially straight path.

In accordance with the second sub-aspect of the first-aspect of thedisclosed embodiment one of the at least one first and at least onesecond guide members is configured to engage one of the first and secondguide rails such that another one of the at least one first and at leastone second guide member is held against another one of the first andsecond guide rails.

In accordance with the second sub-aspect of the first aspect of thedisclosed embodiment the at least one first and at least second guidemembers are configured to interface with a first and second contouredguide members extending from respective ones of the first and secondguide rails where the first and second contoured guide members haveopposing contours for directing a respective one of the at least firstguide member and the at least second guide member into engagement with arespective one of the first and second guide rails.

In accordance with a third sub-aspect of the first aspect of thedisclosed embodiment, the autonomous transport vehicle is configured totravel along at least picking aisles of a storage and retrieval systemand the at least one first guide member and the at least one secondguide member are configured such that the autonomous transport vehiclecan enter the picking aisles with the front of the autonomous transportvehicle leading or trailing a direction of travel of the autonomoustransport vehicle.

In accordance with the third sub-aspect of the first aspect of thedisclosed embodiment, the storage and retrieval system further includesa conveyor interface section, the at least one first guide member andthe at least one second guide member are configured such that theautonomous transport vehicle can enter the conveyor interface sectionwith the front of the autonomous transport vehicle leading or trailing adirection of travel of the autonomous transport vehicle.

In accordance with a second aspect of the disclosed embodiment, anautomated transport vehicle is provided for transporting items in astorage and retrieval system where the storage and retrieval systemincludes picking aisles adjacent item storage locations. The automatedtransport vehicle includes a frame having a front end, a back end and alongitudinal axis extending between the front and back ends. A pair offirst guide members are located on a first side of the frame where oneof the first guide members is located adjacent the front end and theother of the first guide members is located adjacent the back end, eachguide member of the pair of first guide members having a first guidemember frame of reference. A pair of second guide members are located ona second side of the frame, opposite the first side, where one of thesecond guide members is located adjacent the front end and the other ofthe second guide members is located adjacent the back end, each guidemember of the pair of second guide members having a second guide memberframe of reference. The pair of first guide members and the pair ofsecond guide members are asymmetrically compliant so that a stiffness ofeach one of the pair of first guide members in response to a force in apredetermined direction relative to a respective first guide memberframe of reference is different than a stiffness of each one of the pairof second guide members in response to the force in the predetermineddirection relative to a respective second guide member frame ofreference.

In accordance with the second aspect of the disclosed embodiment eachguide member of the pair of first guide members are configured to pivotrelative to the frame when a resultant force applied to the guide wheelis at an angle relative to the longitudinal axis.

In accordance with the second aspect of the disclosed embodiment, thepair of first guide members is configured to maintain the autonomoustransport vehicle at a predetermined distance within the picking aislesfrom items in the storage locations.

In accordance with the second aspect of the disclosed embodiment, thepair of first guide members and the pair of second guide members areconfigured to allow the autonomous transport vehicle to traverse thepicking aisle with either the front end or back end leading a directionof travel through the picking aisle.

In accordance with the second aspect of the disclosed embodiment, thestorage and retrieval system further includes conveyor interfacesections and the pair of first guide members and the pair of secondguide members are configured to allow the autonomous transport vehicleto traverse the conveyor interface section with either the front end orback end leading a direction of travel through the conveyor interfacesection.

In accordance with a third aspect of the disclosed embodiment a storageand retrieval system is provided. The storage and retrieval systemincludes a transfer deck, picking aisles in communication with thetransfer deck, and at least one autonomous transport vehicle configuredto traverse the transfer deck and picking aisles. The at least oneautonomous transport vehicle having a frame with a front end and a backend and a longitudinal axis extending between the front and back endsand at least one first guide member disposed on a first side of theframe and at least one second guide member disposed on a second oppositeside of the frame where the at least one first guide member and the atleast one second guide member are asymmetrically compliant so that astiffness of the at least one first guide member in response to a forcein a predetermined direction relative to the first guide member frame ofreference is different than a stiffness of the at least second guidemember in response to the force in the predetermined direction relativeto the second guide member frame of reference.

In accordance with the third aspect of the disclosed embodiment, the atleast one first guide member includes at least one first guide wheel anda first pivot member rotatably mounted to the frame and the at least onesecond guide member includes at least one second guide wheel and asecond pivot member rotatably mounted to the frame, the at least onefirst guide wheel being rotatably mounted to the first pivot memberwhere an axis of rotation of the first pivot member is locatedtransversely in-line with a rotation axis of the at least one firstguide wheel, and the at least one second guide wheel is rotatablymounted to the second pivot member where an axis of the second pivotmember is longitudinally spaced from an axis of rotation of the at leastone second guide wheel.

In accordance with the third aspect of the disclosed embodiment, thestorage and retrieval system further includes conveyor interfacesections having two transfer deck interfaces with the transfer deckconfigured for autonomous transport-vehicle entry/exit to/from theconveyor interface sections and the autonomous transport vehicle isconfigured to one or more of enter/exit the two transfer deck interfaceswith either of the front and back ends leading a direction of travelthrough the conveyor interface section and enter/exit and traverse thepicking aisles with either of the front and back ends leading adirection of travel through the storage location picking aisles.

In accordance with a fourth aspect of the disclosed embodiment a storageand retrieval system is provided. The storage and retrieval systemincludes storage locations, at least one picking aisle configured toprovide access to each of the storage locations, a transfer deckconfigured to allow substantially mechanically unconstrained travel ofat least one autonomous transport vehicle on the transfer deck, and avehicle guide system configured to at least guide a transition of the atleast one autonomous transport vehicle from substantially mechanicallyunconstrained travel on the transfer deck to substantially mechanicallyconstrained travel within the at least one picking aisle.

In accordance with the a first sub-aspect of the fourth aspect of thedisclosed embodiment, the vehicle guide system includes at least onecurved restraint disposed on at least one side of each of the at leastone picking aisle at a junction between the transfer deck and arespective picking aisles, where the at least one curved restraint isconfigured to interface with guiding members of the autonomous transportvehicle for guiding the autonomous transport vehicle into the pickingaisle.

In accordance with first sub-aspect of the fourth aspect, of thedisclosed embodiment, the vehicle guide system further includes at leastone substantially linear guide member disposed on at least one side ofeach picking aisle where the at least one substantially linear guidemember substantially extends from a respective one of the at least onecurved restraint.

In accordance with the first sub-aspect of the fourth aspect of thedisclosed embodiment, the at least one curved restraint includes a pairof converging restraints disposed on opposite sides of the respectivepicking aisle where the pair of converging constraints converges towardsan entrance of the picking aisle. The vehicle guide system furtherincludes a pair of substantially linear guide member disposed onopposite sides of respective picking aisle where each substantiallylinear guide member extends from a respective one of the convergingrestraints.

It should be understood that the exemplary embodiments disclosed hereincan be used individually or in any suitable combination thereof. Itshould also be understood that the foregoing description is onlyillustrative of the embodiments. Various alternatives and modificationscan be devised by those skilled in the art without departing from theembodiments. Accordingly, the present embodiments are intended toembrace all such alternatives, modifications and variances that fallwithin the scope of the appended claims.

What is claimed is:
 1. A method comprising: providing an autonomous transport vehicle, the autonomous transport vehicle including a frame having a longitudinal axis extending from a front of the frame to a back of the frame; mounting at least one first guide member on one side of the frame, the at least one first guide member having a first guide member frame of reference; and mounting at least one second guide member to an opposite side of the frame than the at least one first guide member, the at least one second guide member having a second guide member frame of reference; wherein the at least one first guide member and the at least one second guide member are asymmetrically compliant guide members so that a stiffness of the at least one first guide member in response to a force in a predetermined direction relative to the first guide member frame of reference is different than a stiffness of the at least one second guide member in response to the force in the predetermined direction relative to the second guide member frame of reference and a stiffness of the at least one first guide member at a respective guide surface in response to a force in a different predetermined direction relative to the first guide member frame of reference is the same as a stiffness of the at least one second guide member at a respective guide surface in response to the force in the different predetermined direction relative to the second guide member frame of reference.
 2. The method of claim 1, further comprising pivotally mounting a first yoke of the at least one first guide member to the frame about a first pivot member and mounting a first engagement member to the first yoke, and pivotally mounting a second yoke of the at least one second guide member to the frame about a second pivot member and mounting a second engagement member to the second yoke.
 3. The method of claim 2, wherein the first engagement member is longitudinally offset from the first pivot member.
 4. The method of claim 2, wherein the second engagement member is transversely aligned with the second pivot member.
 5. The method of claim 1, wherein one or more of the at least one first guide member and the at least one second guide member comprise rotatable wheels.
 6. The method of claim 1, wherein the at least one first guide member comprises two first guide members and the at least one second guide member comprises two second guide members, the method further comprising disposing the two first guide members on a first side of the autonomous transport vehicle and disposing the two second guide members on a second opposite side of the autonomous transport vehicle.
 7. The method of claim 1, further comprising transporting items between the autonomous transport vehicle and storage shelves of a storage and retrieval system and maintaining, with the at least one second guide member, a predetermined transverse distance between the autonomous transport vehicle and items stored on the storage shelves.
 8. The method of claim 1, further comprising guiding the autonomous transport vehicle along a substantially straight path, with the at least one first guide member and the at least one second guide member that are configured to interface with a first guide rail and a second guide rail of a storage and retrieval system where the first guide rail and the second guide rail are located on opposite sides of the autonomous transport vehicle.
 9. The method of claim 8, wherein one of the at least one first guide member and the at least one second guide member is configured to engage one of the first guide rail and the second guide rail such that another one of the at least one first guide member and the at least one second guide member is held against another one of the first guide rail and the second guide rail.
 10. The method of claim 8, further comprising directing a respective one of the at least one first guide member and the at least one second guide member into engagement with a respective one of the first guide rail and the second guide rail, where the at least one first guide member and the at least one second guide member are configured to interface with a first contoured guide member and a second contoured guide member extending from respective ones of the first guide rail and the second guide rail where the first contoured guide member and the second contoured guide member have opposing contours.
 11. The method of claim 1, wherein the autonomous transport vehicle is configured to travel along at least picking aisles of a storage and retrieval system and the at least one first guide member and the at least one second guide member are configured such that the autonomous transport vehicle can enter the picking aisles with a front of the autonomous transport vehicle leading or trailing a direction of travel of the autonomous transport vehicle.
 12. The method of claim 1, wherein the at least one first guide member and the at least one second guide member are configured such that the autonomous transport vehicle can enter a conveyor interface section of a storage and retrieval system with a front of the autonomous transport vehicle leading or trailing a direction of travel of the autonomous transport vehicle.
 13. A method for transporting items in a storage and retrieval system where the storage and retrieval system includes picking aisles adjacent item storage locations, the method comprising: providing an automated transport vehicle including a frame having a front end, a back end and a longitudinal axis extending between the front and back ends; disposing a pair of first guide members on a first side of the frame where one of the pair of first guide members is disposed adjacent the front end and the other of the pair of first guide members is disposed adjacent the back end, each guide member of the pair of first guide members having a first guide member frame of reference; disposing a pair of second guide members on a second side of the frame, opposite the first side, where one of the pair of second guide members is disposed adjacent the front end and the other of the pair of second guide members is disposed adjacent the back end, each guide member of the pair of second guide members having a second guide member frame of reference; and controlling the automated transport vehicle to one or more of enter a picking aisle with the front end leading a direction of travel of the automated transport vehicle to pick or place the items in the storage locations, the automated transport vehicle being guided by one of the pair of first guide members or pair of second guide members, or enter the picking aisle with the back end leading a direction of travel of the automated transport vehicle to pick or place the items in the storage locations, the automated transport vehicle being guided by the other of the pair of first guide members or pair of second guide members; wherein the pair of first guide members and the pair of second guide members are asymmetrically compliant so that a stiffness of each one of the pair of first guide members in response to a force in a predetermined direction relative to a respective first guide member frame of reference is different than a stiffness of each one of the pair of second guide members in response to the force in the predetermined direction relative to a respective second guide member frame of reference.
 14. The method of claim 13, wherein a stiffness of each one of the pair of first guide members at a respective guide surface in response to a force in a different predetermined direction relative to the first guide member frame of reference is the same as a stiffness of each one of the pair of second guide members at a respective guide surface in response to the force in the different predetermined direction relative to the second guide member frame of reference.
 15. The method of claim 13, wherein each guide member of the pair of first guide members is configured to pivot relative to the frame when a resultant force applied to the guide wheel is at an angle relative to the longitudinal axis.
 16. The method of claim 13, further comprising maintaining, with the pair of first guide members, the autonomous transport vehicle at a predetermined distance within the picking aisles from items in the storage locations.
 17. The method of claim 13, wherein the storage and retrieval system further includes conveyor interface sections and the pair of first guide members and the pair of second guide members are configured to allow the autonomous transport vehicle to traverse the conveyor interface section with either the front end or back end leading a direction of travel through the conveyor interface section.
 18. The method of claim 13, wherein one or more of the pair of first guide members and the pair of second guide members comprise rotatable wheels.
 19. The method of claim 13, further comprising guiding the autonomous transport vehicle along a substantially straight path, where the pair of first guide members and the pair of second guide members are configured to interface with a first guide rail and a second guide rail of the storage and retrieval system where the first guide rail and second guide rail are located on opposite sides of the autonomous transport vehicle.
 20. The method of claim 19, wherein one of the pair of first guide members and the pair of second guide members is configured to engage one of the first guide rail and the second guide rail such that another one of the pair of first guide members and the pair of second guide members is held against another one of the first guide rail and the second guide rail. 